Locales: Removed a lot of existing locale handling

There was a lot of locale handling to get correct/expected date
formatting within the app.
Carbon now has built-in locale content rather than us needing to target
specific system locales.

This also removes setting locale via Carbon directly.
Carbon registers its own Laravel service provider which seems to
accurately pull the correct locale from the app.

For #4555

app/Http/Middleware/Localization.php

@@ -27,7 +27,7 @@ class Localization
         view()->share('locale', $userLocale);
 
         // Set locale for system components
-        $this->localeManager->setAppLocale($userLocale);
+        app()->setLocale($userLocale->appLocale());
 
         return $next($request);
     }